Glass filaments usually have a solid cross-section. There are, however, instances where hollow filaments would be preferred, since substantially the same rigidity can be achieved with reduced weight by employing hollow filaments.
U.S. Pat. No. 2,269,459 discloses flame drawing a preformed glass tube into a hollow filament. U.S. Pat. Nos. 4,698,082 and 4,704,149 disclose systems for forming hollow filaments wherein a gas supply tube is positioned in each tip of the feeder to concomitantly supply an annular stream of molten glass and a gas in the interior thereof to form a hollow filament. The gas supply tubes are connected to a header or headers located above the pool of molten glass. Thus, the gas supply tubes are long and subject to various distorting forces. Various intricate systems for attaching the gas supply tubes to or at the feeder tips are disclosed, but such designs are rather complex and require a substantial amount of precious metal to be used.
The present invention provides a feeder capable of producing hollow filaments wherein the stream defining tips are adapted to move the gas from the forming zone into the interior of the forming cone to produce such filaments.